1. Field of the Invention
The present invention relates to a drive control device of vibration wave motor which is configured to obtain a driving force by applying a periodic signal to an electro-mechanical energy conversion element to vibrate a vibration member.
2. Related Background Art
A vibration wave motor is generally composed of a vibration member, which consists of an electro mechanical energy conversion element and an elastic member, and a moving member which is kept in press contact with the vibration member; a driving force is generated in the vibration member by applying a periodic signal (an AC signal) to the electro-mechanical conversion element so as to vibrate the vibration member, thereby to apply a frictional driving force to the moving member so as to obtain movement, such as rotational movement. In the vibration wave motor, a plurality of periodic signals having different phases are applied to the electro-mechanical energy conversion element, thereby forming in the vibration member a plurality of standing waves having different phases, respectively; the plurality of standing waves are synthesized to compose a driving vibration in the vibration member.
As a control device for controlling rotational drive of such a vibration wave motor, there is conventionally known a control device disclosed, for example, by Japanese Patent Application Laid-Open No. 3-18282. The vibration wave motor has a property of changing its rotational speed according to a frequency of the periodic signal applied to the electro-mechanical energy conversion element, and when the vibration wave motor is to be started smoothly, the above described control device first sets a frequency of a periodic signal at a frequency at which the rotational speed of the vibration wave motor is zero, applies a periodic signal having a specified voltage to the electro-mechanical energy conversion element and then gradually changes the frequency of the periodic signal to a frequency corresponding to a desired rotational speed of the vibration wave motor. When the vibration wave motor is to be stopped smoothly, in contrast, the control device first changes the frequency of the periodic signal to the frequency at which the rotational speed of the vibration wave motor is zero and zeroes the specified voltage of the periodic signal. Furthermore, when the vibration wave motor is to be stopped abruptly for positioning, the control device zeroes the specified voltage of the periodic signal without changing the frequency.
Even when the periodic signal has the specified frequency at which the rotational speed of the vibration wave motor is zero, however, the vibration member is generally vibrating while the periodic signal has the specified voltage, whereby a vibration wave motor which is controlled with the above described conventional control device poses a problem that a vibration amplitude of the vibration member changes abruptly and an abnormal noise is produced due to an impact of the abrupt change of the vibration amplitude of the vibration member when a voltage value of the periodic signal is changed from zero to the specified voltage value at a start time and a voltage value of the periodic signal changes from the specified voltage value to zero at a stop time.
The present invention has been derived in view of such a problem, and an object of the present invention is to provide a drive control device of a vibration wave motor which prevents abnormal noise from being produced at a start time and a stop time.
In order to attain the above described object, one aspect of the application is to provide a device which applies, for driving the motor, a voltage lower than a specified voltage value and gradually changes the applying voltage from this condition to the specified voltage value at a vibration wave motor start time.
For the above described object, one aspect of the application is to provide a device which gradually changes the specified voltage value to a voltage value lower than the specified voltage and stops applying the voltage from this condition at a vibration wave motor stop time.
Other objects of the present invention will be apparent from embodiments which are described below with reference to the accompanying drawings.